Solar panel experience. by
Vyv Cox

After two seasons of cruising our Sadler 34 with 150 Ah of
service battery capacity and 75 Ah of starter battery, it was
clear that we needed to do something about keeping them fully
charged. During a glorious fortnight cruising in Cardigan Bay in
1996 we sailed very short daily distances, often without running
the engine at all. Keeping supplies of butter and beer in optimum
condition required us to run the refrigerator constantly, with
the result that battery voltage rarely staggered to 12.5 V and
was more often seen at less than 12.0 V. On some mornings we
would wake (usually quite late) with insufficient service power
to drive the fresh water pump or even to light a light bulb.
Perhaps as a consequence of this abuse, but possibly due to a
lifetime (however brief) of similar treatment, we were forced to
replace one battery in Aberystwyth at a cost of £81. A
later cruise to Scotland was accomplished in far more temperate
conditions, allowing us to turn the refrigerator off at night,
but we had acquired a taste for cold drinks. Something would have
to be done!

The solution arrived in the rather drastic form of a job
transfer to The Netherlands. On a very wintry weekend early in
1997 we attended HISWA, the Dutch Boat Show in Amsterdam. Several
exhibitors were showing solar panels and we collected the usual
stack of literature from each. The most appropriate for our
purpose seemed to be a Sunware 2.0 Amp, 40-cell unit that will
allow a certain amount of bending (3 cm per metre length) and
could be walked upon when screwed down to the deck. 40-cell
panels are intended to provide extra voltage to compensate for
reduced output when hot, a serious flaw in design that
demonstrates once again how the laws of physics conspire against
yachtsmen. A couple of weeks later we visited the supplier, also
in Amsterdam, and made our purchases. In addition to the panel we
bought the cheapest controller available, an 8 Amp unit, with the
future intention of adding more panels. On getting it home and
translating the instructions we found that we would have been
much better off with a more expensive unit (naturally) that
switches from the service battery to the starter battery when the
former is fully charged. So another trip to Amsterdam resulted
and the unit was exchanged for a FOX-i90-2A, a 12 Amp unit that
will certainly cope with anything we can ever hope to supply to
it.

Figure 1.

The panel screwed to the deck abaft the mast, requiring a
slight bowing that is accommodated by the unit. Shadow thrown by
the mast, boom and running rigging has not been found to cause
significant reductions in charging.

On a May visit home to prepare the boat for its voyage to
Holland we fitted the units. We had decided to put the panel in
one of the few available places on the coachroof, astern of the
mast. Although this was likely to be in shadow for some of the
time we chose to accept it as a compromise, not wishing to build
a structure to give maximum exposure.

4 mm2, domestic multi-strand wiring cable was
purchased to give the maximum possible cross-sectional area
consistent with feeding it through some very small holes and
passages. The longest run, about 6 metres, was made between the
solar panel and the control unit, which was placed on the switch
panel behind the companionway steps. Separate cables were led
from the control unit to each battery connector on the main
battery switch, a distance of only 30 cm. Finally the fuses were
put in and we checked the digital ammeter on the control unit.
Nothing! The job had taken such a long time that it was now dark.
On awaking next morning we expectantly viewed the meter and found
a healthy 0.4 Amp, rising to over 1.4 Amp by midday. We then left
the boat until June.

Figure 2. Wiring circuit supplied with the control
unit

Our next look at the meter was very
encouraging; both service and starter batteries indicated almost
13.0 Volts. During the course of our three week cruise from
Anglesey to Holland via Brittany the refrigerator was never off.
Service battery voltage fell to about 12.3 volts during an
overnight passage but recovered during the day. Occasional use of
the engine in calm and to enter ports was sufficient to boost
voltages to over 13.0 and we never ran the engine simply to
charge the batteries. Since then we have enjoyed a remarkably hot
summer during which we have spent every weekend, one four day
weekend and a week's holiday on the boat, largely in temperatures
above 30 degrees Celsius.

The refrigerator has been on constantly during these periods,
although we use shore power to reduce its temperature when we
first arrive and stock it with food at the start of the weekend.
We now use the engine very rarely, perhaps only for half-an-hour
per weekend, yet the lowest service battery voltage yet seen has
been 12.2 V. The starter battery voltage is a constant 12.8 V.
The shadow of the boom is rarely a problem as we simply travel it
to the appropriate side. Mast shadow probably accounts for a
couple of hours per day but has no noticeable effect.

Figure 3.

The Fox-i90 unit, upper left, fitted nicely into the available
space on the panel, although the wiring path was tortuous. Here
it is reading a healthy 0.4 A around midday in early October.

Figure 4.

The control unit in its alternative mode, showing voltage.
Levels as high as the 13.7 V displayed occur only during or
shortly after running the engine.

It would not be possible to justify fitting such equipment
solely on the grounds of battery replacement. The total paid for
panel, controller and cable was nearly £400, enough to
cover likely battery costs for years to come. Its advantage to us
is the knowledge that batteries are always sufficiently charged
for their purpose, that they will remain charged during the
winter and unattended periods without the need for booster
charging and, best of all, the avoidance of those lengthy periods
of engine running at anchor. However, when looked at in terms of
the considerable wear that engine bores suffer during the
unloaded charging process, there may be another side to the
argument. I just enjoy the quiet of the mornings and don't bother
to think about it.